The approach to a runway is one of the most critical and potentially dangerous parts of flying for it is at this time that the aircraft must be flown close to the ground at an attitude (pitch) and air speed very near its stalling point. This fact shows up in the relatively high rate of stall-pin accidents during this phase of the flight.
At present, there is an Instrument Landing System that provides a means of vertical descent guidance. This is the glide slope, a component of the Instrument Landing System which requires the use of highly sophisticated airborne and ground-installed equipment. The only visual aid for pilots is the Visual Approach Slope Indicator (V.A.S.I.) System which is a ground-installed device which uses different colored lights to define predetermined visual approach paths while descending to the runway. It provides the same information visually that the glide slope unit provides electronically. The V.A.S.I System is installed only at relatively few of the larger airports and even then is available only when a particular runway is being used.
For all practical purposes, the average pilot, particularly in smaller aircraft, has no visual aids available for descent guidance when making an approach to a runway and must rely solely on his own experience and judgement. To properly judge an approach, the pilot must sight along an imaginary approach path that forms an angle between the horizon and his line of sight when viewing the desired landing spot. The aircraft is then flown parallel or down the imaginary path to the runway. Convection currents, wind gusts, and terrain features are a few of the unknowns that often cause a pilot to misjudge his approach and miss his landing spot. When making a visual approach to a runway for a landing, the pilot uses the apparent motion of objects on the ground as a guide in judging his descent. However, all objects that move downward will be overshot and all objects that move upward towards the horizon will be undershot. The stationary spot or point of no motion is where the aircraft will land if the flight path is continued unchanged.
It is an object of the present invention to provide a sighting device that frames the desired landing spot within a small area so that the apparent motion is more easily detected and permits the pilot to control his descent in order to make an accurate approach to his desired landing spot.
It is an object of the present invention to provide a self-contained sighting device that is simple and easy to use and independent of any ground-installed equipment, requiring little or no in-flight adjustments to permit the pilot to make a safe approach to a landing site.
It is a further object of the present invention to provide a sighting device that can be preset to indicate a predetermined visual approach path or corridor, permitting a safe landing at any airport or landing site.
It is still further an object of this invention to provide a glide indicator sighting device that employs sighting frames or windows instead of the conventional front and rear sights that require too much of the pilot's attention that will allow the pilot to quickly and easily determine the proper position to begin his descent while automatically directing the pilot's line of sight to parallel the desired approach path.
It is still further an object of this invention to provide a sighting device that will provide an airborne reference point to aid the pilot in his descent to a landing spot while indicating a preset angle of approach regardless of the attitude of the aircraft.